German patent DE 197 56 838 C1 discloses a rotary piston pump with a plurality of rotary piston pairs disposed on parallel shafts. These rotary pistons rotate free from contact and concentrically in the circular housing sections which form the pump chambers. The rotary pistons are connected non-rotatably by means of tongue-and-groove joints to the respective assigned shaft. For this purpose, a feather key is provided in each case, which engages on the one hand in a shaft keyway and on the other hand in a groove of the rotary piston.
German patent application DE 198 06 657 A1 discloses a rotary pump with a pump housing oval in cross-section, with a pair of rotors engaging into one another and disposed in the housing on two parallel shafts capable of being driven in a rotary manner in opposite directions, said rotors each comprising two or more displacement vanes. The displacement vanes rotate with the rotation of the rotors in a sealing manner adjacent to the inner side of the wall of the pump housing and to the respective other rotor. The rotors can be pulled off in the longitudinal direction of the shafts from the latter when the pump housing is opened, the shafts being coupled with one another by torque transmission means, such as a pair of meshing gear wheels or a chain drive or belt drive. One of the shafts can be connected to a drive motor. The rotor pump according to the invention is characterised in that the torque transmission means are constituted with a coupling which is engaged in the basic state and can be disengaged when required.